CN114142021A - Preparation method of polycrystalline positive electrode material modified in tight coating mode - Google Patents

Preparation method of polycrystalline positive electrode material modified in tight coating mode Download PDF

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Publication number
CN114142021A
CN114142021A CN202110565861.4A CN202110565861A CN114142021A CN 114142021 A CN114142021 A CN 114142021A CN 202110565861 A CN202110565861 A CN 202110565861A CN 114142021 A CN114142021 A CN 114142021A
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graphene
polycrystalline
positive electrode
electrode material
coated
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王浩
温宇
卢瑶
徐昊
王欣全
步绍宁
张永龙
杜萍
王哲
刘晓雨
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Ningxia Hanghan Graphene Technology Research Institute Co ltd
Ningxia Hanyao Graphene Energy Storage Material Technology Co ltd
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Ningxia Hanghan Graphene Technology Research Institute Co ltd
Ningxia Hanyao Graphene Energy Storage Material Technology Co ltd
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Publication of CN114142021A publication Critical patent/CN114142021A/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention relates to the field of lithium ion battery electrodes, in particular to a preparation method of a polycrystalline anode material modified in a tight coating mode. A preparation method of a polycrystalline anode material modified in a tight coating mode comprises the steps of mixing the polycrystalline anode material coated with graphene with a conductive agent and a binder, adding N-methyl pyrrolidone to adjust solid content, and coating the mixture on a current collector. The invention provides a preparation method of a polycrystalline anode material modified in a tight coating mode, and the lithium ion battery electrode obtained by the preparation method comprises a special anode material, and the surface of the special anode material is coated with graphene with a specific morphology, so that the graphene coated with the morphology does not change the original crystal phase structure and size of the polycrystalline anode material, the prepared lithium ion battery has the advantages of smaller alternating current impedance, higher cycle capacity retention rate at 45 ℃, higher high-rate charge-discharge capacity retention rate and optimized comprehensive performance.

Description

Preparation method of polycrystalline positive electrode material modified in tight coating mode
Technical Field
The invention belongs to the field of lithium ion battery electrodes, and particularly relates to a preparation method of a polycrystalline anode material modified in a tight coating mode.
Background
With the development of the preparation technology of the lithium ion battery and the related materials thereof in recent years, the lithium ion battery undoubtedly replaces the nickel-hydrogen battery, the lead-acid battery and the like to become a new generation power supply with high technological content and the most extensive application, has the advantages of environmental protection, high energy density, good cycle performance, good safety performance and the like, is called as the most promising chemical power supply, and has become one of the most rapid and active areas of the global lithium ion battery in China. The positive electrode material of the lithium ion battery is one of the key factors determining the performance of the battery, and therefore, under the current situation, the development of the positive electrode material of the lithium ion battery with good thermal safety performance and cycle stability performance is urgent.
Graphene is used as a material with good conductivity, and is very suitable for being used as a coating material to carry out surface modification on a lithium ion positive electrode material. The graphene is unevenly dispersed on the surface of the positive electrode material and can be agglomerated, so that the material has strong oxidizing property in the final charging stage, a large amount of oxygen is released, and the processability and safety performance of the battery are weakened. Therefore, a positive electrode material for promoting graphene to be uniformly and tightly coated on the surface of the positive electrode material is needed, and the service performance of the lithium ion battery is improved.
Disclosure of Invention
In order to solve the problems, the first aspect of the invention provides a preparation method of a modified polycrystalline positive electrode material in a close coating mode, which comprises the steps of mixing the graphene-containing coated polycrystalline positive electrode material with a conductive agent and a binder, adding N-methyl pyrrolidone to adjust the solid content, and coating the mixture on a current collector to prepare the modified polycrystalline positive electrode material; the graphene-coated polycrystalline positive electrode material, the conductive agent and the binder are mixed according to the mass ratio of (90-99): (0.5-5): (0.5-5).
As a preferable technical solution, the conductive agent is selected from one or more of a carbon-based material, a metal-based material, and a conductive polymer.
As a preferable technical scheme, the binder is selected from one or more of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, polyvinyl fluoride, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin and nylon.
As a preferred technical solution, the current collector is an aluminum foil.
As a preferable technical scheme, the graphene-coated polycrystalline positive electrode material is mixed with a conductive agent and a binder, and then N-methyl pyrrolidone is added to adjust the solid content to 30-70%.
As a preferred technical scheme, a TEM image of the graphene-coated polycrystalline cathode material meets the requirements of attached figures 1-3; and SEM images of the graphene-coated polycrystalline cathode material meet the requirements of attached figures 4-6.
As a preferable technical scheme, the coating thickness of graphene on the surface of the polycrystalline positive electrode material in the graphene-coated polycrystalline positive electrode material is less than 10 nm.
As a preferred technical scheme, graphene in the graphene-coated polycrystalline positive electrode material is closely attached to the surface of the positive electrode material, and the attachment gap is smaller than 3 nm; preferably, the fit clearance between graphene in the graphene-coated polycrystalline positive electrode material and the surface of the positive electrode material is almost 0 nm.
As a preferable technical scheme, an included angle between graphene in the graphene-coated polycrystalline positive electrode material and a tangent line of the graphene at a contact point of the positive electrode material is less than 5 degrees; preferably, the included angle between the graphene in the graphene-coated polycrystalline positive electrode material and the tangent line of the graphene at the contact point of the positive electrode material is almost 0 °.
As a preferred technical solution, the X-ray test results of the polycrystalline cathode material coated with graphene and the polycrystalline cathode material are consistent, the pattern of the polycrystalline cathode material coated with graphene is substantially the same as the pattern peak shape of the polycrystalline cathode material, the relative intensity distribution order is substantially the same, and the overall shift angle of the diffraction peak is less than 3 °.
As a preferred technical solution, the particle size distribution results of the graphene-coated polycrystalline positive electrode material and the polycrystalline positive electrode material are consistent.
As a preferred technical solution, the preparation step of the tightly-coated modified polycrystalline positive electrode material comprises: mixing glue solution containing graphene with a positive active substance to obtain slurry, and drying the slurry to obtain a positive material; the positive active material exhibits a polycrystalline morphology comprising LiCoO2And/or LiNixCoyMnzO2And/or LiNixCoyAlzO2X + y + z is 1, x is more than or equal to 0.2 and less than or equal to 0.95, y is more than or equal to 0.05 and less than or equal to 0.4, and z is more than or equal to 0.05 and less than or equal to 0.5; the crystal structure is layered and belongs to the R-3m space group.
As a preferable technical scheme, the glue solution containing graphene and the positive electrode active material are mixed by an organic solvent a, and then the viscosity is adjusted by an organic solvent B to obtain the slurry.
As a preferred technical scheme, the glue solution containing graphene comprises a binder, graphene and a solvent A; and the mass ratio of the binder to the graphene to the solvent A is (5-10): (2-8): (82-93).
As a preferred technical scheme, the organic solvent A comprises a binder and a solvent B; and the mass ratio of the binder to the solvent B is (5-15): (85-95).
In a preferred embodiment, the organic solvent B is selected from one or more of benzene, toluene, acetone, methyl ethyl ketone, N-methylpyrrolidone (NMP), and dimethylformamide.
As a preferable technical scheme, the mixing temperature is 20-80 ℃ in the mixing process of the slurry.
As a preferred technical solution, the slurry drying method is selected from any one of heating drying, spray drying, freeze drying, vacuum rotary drying, microwave drying, forced air drying and transmission drying.
As a preferred technical solution, the spray drying: the temperature of the air inlet is 350-500 ℃, and the temperature of the outlet is 120-300 ℃.
Has the advantages that: the invention provides a preparation method of a polycrystalline anode material modified in a tight coating mode, and the lithium ion battery electrode obtained by the preparation method comprises a special anode material, and the surface of the special anode material is coated with graphene with a specific morphology, so that the graphene coated with the morphology does not change the original crystal phase structure and size of the polycrystalline anode material, the prepared lithium ion battery has smaller alternating current impedance, and the cycle capacity retention rate at 45 ℃ and the high-rate charge-discharge capacity retention rate are higher, so that the comprehensive performance of the battery is very excellent.
Drawings
FIG. 1: a TEM image of the nano-scaled graphene coated polycrystalline positive electrode material of example 1;
FIG. 2: a TEM image of the micron-sized graphene-coated polycrystalline positive electrode material of example 2;
FIG. 3: a TEM image of the micro-nano-scale graphene-coated polycrystalline positive electrode material of example 3;
FIG. 4: SEM image of nano-scaled graphene-coated polycrystalline positive electrode material of example 1;
FIG. 5: SEM image of micron-sized graphene-coated polycrystalline positive electrode material of example 2;
FIG. 6: SEM image of micro-nano-scaled graphene-coated polycrystalline positive electrode material of example 3;
FIG. 7: XRD patterns of the cathode materials of example 1 and comparative example; the method comprises the following steps of (1) coating a nano-scale graphene-coated polycrystalline positive electrode material, and (ii) coating a pre-coated polycrystalline positive electrode material;
FIG. 8: XRD patterns of the polycrystalline positive electrode materials of example 2 and comparative example; the method comprises the following steps of (1) coating a polycrystalline anode material by micron-sized graphene, and (ii) coating a polycrystalline anode material before coating;
FIG. 9: XRD patterns of the polycrystalline positive electrode materials of example 3 and comparative example; the method comprises the following steps of (1) coating a micro-nano graphene-coated polycrystalline positive electrode material, and (ii) coating a pre-coated polycrystalline positive electrode material;
FIG. 10: grain size distribution plots of the polycrystalline positive electrode materials of example 1 and comparative example;
FIG. 11: grain size distribution plots of the polycrystalline positive electrode materials of example 2 and comparative example;
FIG. 12: grain size distribution plots of the polycrystalline positive electrode materials of example 3 and comparative example;
FIG. 13: raman plots (a) and (b) of the nano-scaled graphene-coated polycrystalline positive electrode material of example 1;
FIG. 14: raman plots (a) and (b) of the micron-sized graphene-coated polycrystalline positive electrode material of example 2;
FIG. 15: raman graphs (a) and (b) of the micro-nano-scale graphene-coated polycrystalline positive electrode material of example 3;
FIG. 16: electrochemical ac impedance spectra of the resulting cells of example 1 and comparative example; the method comprises the following steps of (1) coating a nano-scale graphene-coated polycrystalline positive electrode material, and (ii) coating a pre-coated polycrystalline positive electrode material;
FIG. 17: electrochemical ac impedance spectra of the resulting cells of example 2 and comparative example; the method comprises the following steps of (1) coating a polycrystalline anode material by micron-sized graphene, and (ii) coating a polycrystalline anode material before coating;
FIG. 18: electrochemical ac impedance spectra of the resulting cells of example 3 and comparative example; the method comprises the following steps of (1) coating a micro-nano graphene-coated polycrystalline positive electrode material, and coating a pre-coated polycrystalline positive electrode material;
FIG. 19: the 45 ℃ cycle capacity retention of the resulting batteries of example 1 and comparative example; the method comprises the following steps of (1) coating a polycrystalline positive electrode material by using nano-scale graphene, and (1) coating a polycrystalline positive electrode material before coating;
FIG. 20: the 45 ℃ cycle capacity retention ratio of the batteries obtained in example 2 and comparative example; the method comprises the following steps of (1) coating a polycrystalline positive electrode material by micron-sized graphene, and coating a polycrystalline positive electrode material before coating;
FIG. 21: the 45 ℃ cycle capacity retention of the resulting batteries of example 3 and comparative example; the method comprises the following steps of (1) coating a micro-nano graphene-coated polycrystalline positive electrode material, and coating a pre-coated polycrystalline positive electrode material;
FIG. 22: rate charge capacity retention rate (a) and rate discharge capacity retention rate (b) of the button cell of example 1 and comparative example; the method comprises the following steps of (1) coating a polycrystalline positive electrode material by using nano-scale graphene, and (1) coating a polycrystalline positive electrode material before coating;
FIG. 23: rate charge capacity retention rate (a) and rate discharge capacity retention rate (b) of the button cell of example 2 and comparative example; the method comprises the following steps of (1) coating a polycrystalline positive electrode material by micron-sized graphene, and coating a polycrystalline positive electrode material before coating;
FIG. 24: rate charge capacity retention rate (a) and rate discharge capacity retention rate (b) of the button cell of example 3 and comparative example; the method comprises the following steps of (1) coating a micro-nano graphene-coated polycrystalline positive electrode material, and coating a pre-coated polycrystalline positive electrode material;
FIG. 25: a schematic structural diagram of a graphene-coated single crystal positive electrode material; wherein, a is a schematic diagram of the graphene sheet diameter-attached single crystal anode material provided by the invention, and b is a schematic diagram of the graphene sheet diameter-attached single crystal anode material in the traditional technology; 1. 3 represents a graphene sheet diameter, and 2 and 4 represent single crystal positive electrode materials.
Detailed Description
The technical features of the technical solutions provided by the present invention are further clearly and completely described below with reference to the specific embodiments, and the scope of protection is not limited thereto.
The words "preferred", "more preferred", and the like, in the present invention refer to embodiments of the invention that may provide certain benefits, under certain circumstances. However, other embodiments may be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, nor is it intended to exclude other embodiments from the scope of the invention.
When a range of values is disclosed herein, the range is considered to be continuous and includes both the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values of the range is included. Further, when multiple range-describing features or characteristics are provided, the ranges may be combined. In other words, unless otherwise indicated, all ranges disclosed herein are to be understood to encompass any and all subranges subsumed therein. For example, a stated range from "1 to 10" should be considered to include any and all subranges between the minimum value of 1 and the maximum value of 10. Exemplary subranges of the range 1 to 10 include, but are not limited to, 1 to 6.1, 3.5 to 7.8, 5.5 to 10, and the like.
In order to solve the problems, the first aspect of the invention provides a preparation method of a modified polycrystalline positive electrode material in a close coating mode, which comprises the steps of mixing the graphene-containing coated polycrystalline positive electrode material with a conductive agent and a binder, adding N-methyl pyrrolidone to adjust the solid content, and coating the mixture on a current collector to prepare the modified polycrystalline positive electrode material; the graphene-coated polycrystalline positive electrode material, the conductive agent and the binder are mixed according to the mass ratio of (90-99): (0.5-5): (0.5 to 5); more preferably, the graphene-coated polycrystalline positive electrode material, the conductive agent and the binder are mixed according to a mass ratio of 94: 3: 3.
preferably, the coating thickness of graphene on the surface of the polycrystalline positive electrode material in the graphene-coated polycrystalline positive electrode material is less than 10 nm.
Preferably, the TEM images of the graphene-coated polycrystalline positive electrode-containing material satisfy fig. 1-3; and SEM pictures of the polycrystalline cathode material coated with the graphene meet the requirements of attached figures 4-6, namely the graphene sheet material shown in the figures is in a close-fit coating state on the surface of the polycrystalline cathode material.
Preferably, the difference between the average particle size of the graphene-containing coated single crystal cathode material and the average particle size of the cathode material is less than 1000 nm; more preferably, the difference between the average particle size of the graphene-containing coated single crystal cathode material and the average particle size of the cathode material is less than 700 nm; most preferably, the difference between the average particle size of the graphene-inclusive coated single crystal positive electrode material and the average particle size of the positive electrode material is less than 500 nm.
Preferably, the X-ray test results of the polycrystalline cathode material coated with graphene and the polycrystalline cathode material are substantially consistent, as shown in fig. 7-9, the pattern of the polycrystalline cathode material coated with graphene is substantially the same as the pattern peak shape of the polycrystalline cathode material, the relative intensity distribution order is substantially the same, and the overall shift angle of the diffraction peak is less than 3 °.
Preferably, the particle size distribution results of the graphene-coated polycrystalline positive electrode material and the polycrystalline positive electrode material are consistent, as shown in fig. 10 to 12; consistency as described herein does not mean complete consistency, but rather substantial consistency. By substantially consistent is meant little or no change.
Preferably, graphene in the graphene-coated polycrystalline positive electrode material is closely attached to the surface of the positive electrode material, and the attachment gap is smaller than 3 nm; more preferably, the fit gap between graphene in the graphene-coated polycrystalline positive electrode material and the surface of the positive electrode material is almost 0 nm.
Preferably, the included angle between the graphene in the graphene-coated polycrystalline positive electrode material and the tangent line of the graphene at the contact point of the positive electrode material is less than 5 degrees; more preferably, the included angle between the graphene in the graphene-coated polycrystalline positive electrode material and the tangent line of the graphene at the contact point of the positive electrode material is almost 0 °.
Preferably, through a combination of laser Raman (Raman) and scanning electron microscopy testing techniques, as shown in fig. 13-15, the non-coating region and the coating region of the polycrystalline positive electrode material containing graphene coating can be distinguished, wherein the D peak, the G peak and the G ' peak in the coating region respectively completely correspond to the D peak, the G peak and the G ' peak of graphene, and the non-coating region is free of the D peak, the G peak and the G ' peak of graphene.
Preferably, as shown in FIGS. 13-15, the laser Raman spectrum of graphene has a value of 0.01. ltoreq. Intensity (D)/Intensity (G). ltoreq.10, and a value of 0.01. ltoreq. Intensity (D)/Intensity (D'). ltoreq.10; more preferably 0.01. ltoreq. Intensity (D)/Intensity (G). ltoreq.5, 0.01. ltoreq. Intensity (D)/Intensity (D'). ltoreq.5; most preferably 0.01. ltoreq. Intensity (D)/Intensity (G). ltoreq.1, 0.01. ltoreq. Intensity (D)/Intensity (D'). ltoreq.1.
Preferably, the conductive agent is selected from one or more of a carbon-based material, a metal-based material, and a conductive polymer.
The carbon-based material such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or the like; metal-based materials such as metal powders or metal fibers of copper, nickel, aluminum, silver, or the like; conductive polymers such as polyphenylene derivatives and the like.
Preferably, the binder is selected from one or more of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, polyvinyl fluoride, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon.
More preferably, the binder is polyvinylidene fluoride.
The current collector may be an aluminum foil, a nickel foil, or a combination thereof, but is not limited thereto.
Preferably, the preparation method of the graphene-coated polycrystalline positive electrode material comprises the following steps: mixing glue solution containing graphene with a positive active substance to obtain slurry, and drying the slurry to obtain a positive material; the positive electrode activityThe material exhibited polycrystalline morphology, including LiCoO2And/or LiNixCoyMnzO2And/or LiNixCoyAlzO2X + y + z is 1, x is more than or equal to 0.2 and less than or equal to 0.95, y is more than or equal to 0.05 and less than or equal to 0.4, and z is more than or equal to 0.05 and less than or equal to 0.5; the crystal structure is layered and belongs to the R-3m space group.
Preferably, the viscosity of the mixed slurry is 100-8000 cp; more preferably, the viscosity is 2500 cp.
The viscosity described herein refers to kinematic viscosity, and is measured at room temperature using a rotary viscometer.
Preferably, the glue solution containing graphene and the positive electrode active material are mixed through an organic solvent A, and then the viscosity is adjusted through an organic solvent B to obtain the slurry.
More preferably, the volume ratio of the graphene-containing glue solution, the positive electrode active material and the organic solvent A is (5-15): (5-10): (80-95) mixing; more preferably, the volume ratio of the glue solution containing graphene, the positive electrode active material and the organic solvent A is (6-10): (6-10): (80-90); most preferably, the volume ratio of the glue solution containing graphene, the positive electrode active material and the organic solvent A is 9: 8: 83.
preferably, the glue solution containing graphene comprises a binder, graphene and a solvent A; and the mass ratio of the binder to the graphene to the solvent A is (5-10): (2-8): (82-93); more preferably, the mass ratio of the binder to the graphene to the solvent A is (7-10): (4-6): (83-85); most preferably, the mass ratio of the binder to the graphene to the solvent A is 9: 5: 86.
preferably, the solvent A is selected from one or more of benzene, toluene, acetone, methyl ethyl ketone, N-methyl pyrrolidone (NMP) and dimethylformamide.
Preferably, the organic solvent A comprises a binder and a solvent B; and the mass ratio of the binder to the solvent B is (5-15): (85-95); more preferably, the mass ratio of the binder to the solvent B is (5-10): (90-95); most preferably, the mass ratio of the binder to the solvent B is 1: 9.
preferably, the solvent B is selected from one or more of benzene, toluene, acetone, methyl ethyl ketone, N-methyl pyrrolidone (NMP) and dimethylformamide; more preferably, the solvent B is N-methylpyrrolidone.
Preferably, the organic solvent B is selected from one or more of benzene, toluene, acetone, methyl ethyl ketone, N-methyl pyrrolidone (NMP) and dimethylformamide; more preferably, the organic solvent B is N-methylpyrrolidone.
Preferably, in the mixing process of the slurry, the mixing temperature is 20-80 ℃; more preferably, the mixing temperature is 20 to 30 ℃.
Preferably, the slurry is dried by any one method selected from heating drying, spray drying, freeze drying, vacuum rotary drying, microwave drying, forced air drying and transmission drying.
Preferably, the spray drying: the temperature of the air inlet is 350-500 ℃, and the temperature of the outlet is 120-300 ℃.
Preferably, the graphene is selected from one or more of nanoscale graphene, micron-scale graphene and micro-nanoscale graphene.
Preferably, the sheet diameter of the graphene is 0.01-30 μm; more preferably, the sheet diameter of the nano-grade graphene is 10-1000 nm; more preferably, the sheet diameter of the micron-sized graphene is 1-30 mu m; more preferably, the micro-nano graphene has a sheet diameter of 200nm to 15 μm.
The inventor finds that how to improve the cycle retention rate of the battery is a difficult point in the research process of the scheme, and the scheme of the invention explains that the inventor guarantees that the graphene sheet material presents a coating form on the surface of the crystal particle of the positive electrode material by controlling the characteristics of the graphene such as sheet diameter, thickness, shape and the like; and when the graphene sheet is in a close-fit coating state on the surface of the crystal particles of the polycrystalline material, the difficulty can be obviously solved, and the embodiment shows that after 150 cycles, compared with the polycrystalline anode material before coating, the cycle retention rate of the coated battery can be improved by 7-15 percentage points, and the cycle retention rate of the battery can reach more than 85%.
Compared with the expansion phenomenon of the charge-discharge volume of the spherical graphene, the expansion phenomenon of the charge-discharge volume of the graphene sheet is more serious, the specific graphene is adopted, multilayer mixing treatment is preferably adopted under the condition that the proper coating form and coating degree are ensured, the graphene is uniformly dispersed among anode material particles through high-speed nano dispersion, and the graphene on the surface of the anode plays a role in fixing oxygen atoms on the surface of the material, so that the material structure is stabilized, the decomposition of electrolyte on the surface of the anode is inhibited, and the cycle performance, especially the high-temperature cycle performance, of the material is improved.
As shown in a of fig. 25, the graphene sheet of the present invention can be well attached to the surface of the polycrystalline positive electrode material, the graphene sheet is in close contact with the polycrystalline positive electrode material without a gap, and the attachment gap between the graphene and the surface of the polycrystalline positive electrode material is about 0 nm; in a reverse view of b in fig. 25, the graphene sheet is often obliquely coated on the surface of the polycrystalline positive electrode material, and a larger degree of adhesion cannot be ensured, which means that when the positive electrode material is coated with graphene having the same surface area, the contact area or the coating area of the surface of the obliquely coated positive electrode material is smaller, and a gap is formed between the obliquely coated positive electrode material and the positive electrode material, and the adhesion gap between the nano-scale graphite and the surface of the positive electrode material is far larger than 3nm, and the close adhesion between the graphene and the positive electrode material according to the present invention is not achieved, and is not within the range of the present invention in which the graphene sheet is in a coating state on the surface of the crystal particle of the positive electrode material.
The applicant also finds that in the case that the graphene sheet material is in a close-fitting coating state on the surface of the crystal particle of the positive electrode material, the graphene sheet material, the positive electrode material and the positive electrode material coated with the graphene have great similarity in performance, that is, the error range of the result obtained by the same characterization means is small, and the application will also specifically explain the method.
The present invention will now be described in detail by way of examples, and the starting materials used are commercially available unless otherwise specified.
Examples
Example 1
Embodiment 1 provides a preparation method of a polycrystalline positive electrode material modified in a tight coating mode, which comprises the steps of mixing the polycrystalline positive electrode material coated with graphene with a conductive agent and a binder, adding N-methylpyrrolidone to adjust the solid content to 50%, and coating the mixture on a current collector to obtain the modified polycrystalline positive electrode material; the graphene-coated polycrystalline positive electrode material, the conductive agent and the binder are mixed according to a mass ratio of 94: 3: 3; wherein the conductive agent is carbon black (litx 200 of Cabot corporation); the binder is polyvinylidene fluoride (HSV 900 of arkema); the current collector is aluminum foil (1N 00-H18 of five-star company);
the preparation method of the graphene-coated polycrystalline positive electrode material comprises the following steps: at room temperature, mixing a binder and a solvent B according to a mass ratio of 1: 9 mixing to form an organic solvent A; the preparation method comprises the following steps of (1) mixing a binder, graphene and a solvent A according to a mass ratio of 9: 5: 86 to form glue solution containing graphene; and finally, mixing the glue solution containing the graphene, the positive electrode active substance and the organic solvent A according to the volume ratio of 9: 8: 83 mixing and adjusting the viscosity to 2500cp by an organic solvent B to obtain slurry; the slurry was then spray dried: the inlet temperature was 420 ℃ and the outlet temperature was 250 ℃.
Wherein the solvent B, the solvent A and the organic solvent B are all N-methyl pyrrolidone;
the positive active substance is YHF-10F type nickel cobalt lithium manganate produced by Ningxia Yao graphene energy storage materials science and technology Limited, belongs to a ternary material, is in a polycrystalline shape, primary particles are agglomerated into secondary particle balls, and D50 of the secondary particle balls is (12 +/-1.5) mu m;
the graphene is nano-scale graphene; the nano-scale graphene is purchased from graphene of model GRCP101S of tianjin exkhegen graphene technologies ltd;
fig. 1 and 4 are TEM and SEM images, respectively, of a nano-scaled graphene-coated polycrystalline positive electrode material; wherein the longest distance between the nano-scale graphene and the surface of the polycrystalline anode material is almost 0 nm; the included angle between the nano-scale graphene and the tangent line of the nano-scale graphene at the contact point of the nano-scale graphene and the positive electrode material is almost 0 degree, which indicates that the nano-scale graphene sheet material is in a close-fit coating state on the surface of the polycrystalline positive electrode material;
fig. 7 is an X-ray diffraction pattern of a nano-scaled graphene-coated polycrystalline positive electrode material; the spectrum of the polycrystalline positive electrode material coated by the nano-grade graphene is basically the same as the spectrum peak shape of the polycrystalline positive electrode material, the relative intensity distribution sequence is basically the same, the integral deviation angle of a diffraction peak is almost 0 degrees, and the fact that the nano-grade graphene sheet is coated on the surface of crystal particles of the polycrystalline material is shown, and the bulk phase structure in the crystal particles of the polycrystalline material is not influenced;
fig. 10 is a graph of grain size distribution of a nano-scaled graphene coated polycrystalline positive electrode material and a positive electrode material; the grain size distribution results of the polycrystalline anode material (green lines) coated by the nano-grade graphene and the polycrystalline anode material (blue lines) before coating are basically consistent, which indicates that the grain size of crystal grains is not obviously increased by the polycrystalline anode material coated by the nano-grade graphene;
fig. 13 is a Raman spectrum of a nano-graphene coated polycrystalline positive electrode material; by laser Raman (Raman) testing technique, it is possible to distinguish the non-cladding region (polycrystalline positive electrode material portion) and the cladding region (nano-scaled graphene-clad polycrystalline positive electrode material) portion, as shown in fig. 13, (a) the red region is the cladding region, and the blue region is the non-cladding region; from the graph (b), it is seen that the D, G and G ' peaks in the coating region completely correspond to the D, G and G ' peaks of graphene, respectively, while the non-coating region has no graphene D, G and G ' peaks.
Example 2
Embodiment 2 provides a preparation method of a polycrystalline positive electrode material modified in a tight coating mode, which comprises the steps of mixing the polycrystalline positive electrode material coated with graphene with a conductive agent and a binder, adding N-methylpyrrolidone to adjust the solid content to 50%, and coating the mixture on a current collector to obtain the modified polycrystalline positive electrode material; the graphene-coated polycrystalline positive electrode material, the conductive agent and the binder are mixed according to a mass ratio of 94: 3: 3; wherein the conductive agent is carbon black (litx 200 of Cabot corporation); the binder is polyvinylidene fluoride (HSV 900 of arkema); the current collector is aluminum foil (1N 00-H18 of five-star company);
the preparation method of the graphene-coated polycrystalline positive electrode material comprises the following steps: at room temperature, mixing a binder and a solvent B according to a mass ratio of 1: 9 mixing to form an organic solvent A; the preparation method comprises the following steps of (1) mixing a binder, graphene and a solvent A according to a mass ratio of 9: 5: 86 to form glue solution containing graphene; and finally, mixing the glue solution containing the graphene, the positive electrode active substance and the organic solvent A according to the volume ratio of 9: 8: 83 mixing and adjusting the viscosity to 2500cp by an organic solvent B to obtain slurry; the slurry was then spray dried: the inlet temperature was 420 ℃ and the outlet temperature was 250 ℃.
Wherein the solvent B, the solvent A and the organic solvent B are all N-methyl pyrrolidone;
the positive active substance is YHF-10F type nickel cobalt lithium manganate produced by Ningxia Yao graphene energy storage materials science and technology Limited, belongs to a ternary material, is in a polycrystalline shape, primary particles are agglomerated into secondary particle balls, and D50 of the secondary particle balls is (12 +/-1.5) mu m;
the graphene is micron-sized graphene; the micron-sized graphene is purchased from graphene of model GRCP0130L of Tianjin Ikekan graphene science and technology Limited;
fig. 2 and 5 are a TEM image and an SEM image of the micron-sized graphene-coated polycrystalline positive electrode material, respectively; wherein the longest distance between the micron-sized graphene and the surface of the polycrystalline anode material is almost 0 nm; the included angle between the micron-sized graphene and the tangent line of the micron-sized graphene at the contact point of the anode material is almost 0 degrees, which shows that the micron-sized graphene sheet material is in a close-fitting coating state on the surface of the polycrystalline anode material;
fig. 8 is an X-ray diffraction pattern of a micron-sized graphene-coated polycrystalline positive electrode material; the spectrum of the polycrystalline positive electrode material coated by the micron-sized graphene is basically the same as the spectrum peak shape of the polycrystalline positive electrode material, the relative intensity distribution sequence is basically the same, the integral deviation angle of a diffraction peak is almost 0 degrees, and the fact that the micron-sized graphene sheet is coated on the surface of crystal particles of the polycrystalline material is shown, and the bulk phase structure in the crystal particles of the polycrystalline material is not influenced;
fig. 11 is a graph of the grain size distribution of a micron-sized graphene coated polycrystalline positive electrode material and a positive electrode material; the grain size distribution results of the polycrystalline anode material coated by the micron-sized graphene (green lines) and the polycrystalline anode material coated by the micron-sized graphene (blue lines) are basically consistent, which shows that the grain size of crystal particles is not obviously increased by the polycrystalline anode material coated by the micron-sized graphene;
fig. 14 is a Raman spectrum of a polycrystalline positive electrode material coated with micron-sized graphene; through a laser Raman (Raman) test technique, a non-coating region (polycrystalline positive electrode material part) and a coating region (polycrystalline positive electrode material coated by micron-sized graphene) part can be distinguished, as shown in fig. 14, (a) a red region is a coating region, and a blue region is a non-coating region; from the graph (b), it is seen that the D, G and G ' peaks in the coating region completely correspond to the D, G and G ' peaks of graphene, respectively, while the non-coating region has no graphene D, G and G ' peaks.
Example 3
Embodiment 3 provides a preparation method of a polycrystalline positive electrode material modified in a tight coating manner, which comprises the steps of mixing the polycrystalline positive electrode material coated with graphene with a conductive agent and a binder, adding N-methylpyrrolidone to adjust the solid content to 50%, and coating the mixture on a current collector to obtain the modified polycrystalline positive electrode material; the graphene-coated polycrystalline positive electrode material, the conductive agent and the binder are mixed according to a mass ratio of 94: 3: 3; wherein the conductive agent is carbon black (litx 200 of Cabot corporation); the binder is polyvinylidene fluoride (HSV 900 of arkema); the current collector is aluminum foil (1N 00-H18 of five-star company);
the preparation method of the graphene-coated polycrystalline positive electrode material comprises the following steps: at room temperature, mixing a binder and a solvent B according to a mass ratio of 1: 9 mixing to form an organic solvent A; the preparation method comprises the following steps of (1) mixing a binder, graphene and a solvent A according to a mass ratio of 9: 5: 86 to form glue solution containing graphene; and finally, mixing the glue solution containing the graphene, the positive electrode active substance and the organic solvent A according to the volume ratio of 9: 8: 83 mixing and adjusting the viscosity to 2500cp by an organic solvent B to obtain slurry; the slurry was then spray dried: the inlet temperature was 420 ℃ and the outlet temperature was 250 ℃.
Wherein the solvent B, the solvent A and the organic solvent B are all N-methyl pyrrolidone;
the positive active substance is YHF-10F type nickel cobalt lithium manganate produced by Ningxia Yao graphene energy storage materials science and technology Limited, belongs to a ternary material, is in a polycrystalline shape, primary particles are agglomerated into secondary particle balls, and D50 of the secondary particle balls is (12 +/-1.5) mu m;
the graphene is micro-nano graphene; graphene of the micro-nano graphene Tianjin Ikewin graphene science and technology Co., Ltd, model GRCP 215Z;
fig. 3 and 6 are TEM and SEM images of the micro-nano-scale graphene-coated polycrystalline positive electrode material, respectively; wherein the longest distance between the micro-nano graphene and the surface of the polycrystalline anode material is almost 0 nm; the included angle between the micro-nano graphene and the tangent line of the micro-nano graphene at the contact point of the micro-nano graphene on the cathode material is almost 0 degrees, which indicates that the micro-nano graphene sheet material is in a close-fitting coating state on the surface of the polycrystalline cathode material;
fig. 9 is an X-ray diffraction pattern of a micro-nano graphene-coated polycrystalline positive electrode material; the spectrum of the polycrystalline positive electrode material coated by the micro-nano graphene is basically the same as the spectrum peak shape of the polycrystalline positive electrode material, the relative intensity distribution sequence is basically the same, the integral deviation angle of a diffraction peak is almost 0 degrees, and the fact that the micro-nano graphene sheet is coated on the surface of crystal particles of the polycrystalline material is shown, and the bulk phase structure in the crystal particles of the polycrystalline material is not influenced;
fig. 12 is a graph of the grain size distribution of the micro-nano graphene-coated polycrystalline positive electrode material and the positive electrode material; the grain size distribution results of the micro-nano graphene-coated polycrystalline positive electrode material (green lines) and the polycrystalline positive electrode material (blue lines) before coating are basically consistent, and the grain size of crystal grains is not obviously increased by the micro-nano graphene-coated polycrystalline positive electrode material;
fig. 15 is a Raman spectrum of a micro-nano graphene-coated polycrystalline positive electrode material; through a laser Raman (Raman) test technology, a non-coating region (polycrystalline positive electrode material part) and a coating region (micro-nano-scale graphene coated polycrystalline positive electrode material) part can be distinguished, as shown in fig. 15, (a) a red region is a coating region, and a blue region is a non-coating region; as can be seen from the graph (b), the D peak, G peak, and G ' peak of the micro-nano-sized graphene-coated polycrystalline positive electrode material in the coating region completely correspond to the D peak, G peak, and G ' peak of graphene, respectively, while the non-coating region does not have the D peak, G peak, and G ' peak of graphene.
Comparative example
The comparative example provides a preparation method of a lithium ion battery electrode containing a polycrystalline anode material, which comprises the steps of mixing the polycrystalline anode material with a conductive agent and a binder, adding N-methyl pyrrolidone to adjust the solid content to 50%, and coating the mixture on a current collector to prepare the lithium ion battery electrode containing the polycrystalline anode material; the polycrystalline-containing positive electrode material, the conductive agent and the binder are mixed according to the mass ratio of 94: 3: 3; wherein the conductive agent is carbon black (litx 200 of Cabot corporation); the binder is polyvinylidene fluoride (HSV 900 of arkema); the current collector is aluminum foil (1N 00-H18 of five-star company);
the preparation method of the polycrystalline-containing cathode material comprises the following steps: at room temperature, mixing a binder and a solvent B according to a mass ratio of 1: 9 mixing to form an organic solvent A; mixing a binder and a solvent A according to a mass ratio of 12: 88 to form glue solution; and finally, mixing the glue solution, the positive active substance and the organic solvent A according to a volume ratio of 9: 6: 85, mixing the components, and adjusting the viscosity to 2500cp by an organic solvent B to obtain slurry; the slurry was then spray dried: the temperature of an air inlet is 420 ℃, and the temperature of an outlet is 250 ℃; wherein the solvent B, the solvent A and the organic solvent B are all N-methyl pyrrolidone.
Performance evaluation
The preparation method of the button cell comprises the following steps: the electrode plates prepared in the embodiment and the comparative example are dried in a vacuum drying oven at 110 ℃ for 4-5 hours for later use. And rolling the pole piece on a rolling machine, and punching the rolled pole piece into a circular pole piece with a proper size. The cell assembly was carried out in a glove box filled with argon, the electrolyte of the electrolyte was 1M LiPF6, the solvent was EC: DEC: DMC is 1:1:1 (volume ratio), and the metal lithium sheet is the counter electrode. The capacity test was performed on a blue CT model 2001A tester.
The electrochemical alternating current impedance of the batteries obtained in the examples 1, 2 and 3 and the comparative example is tested at room temperature of 25 ℃, and the experimental results are respectively shown in fig. 16, 17 and 18; performing charge-discharge cycle test at a high temperature of 45 ℃ at a charge-discharge rate of 0.5C/0.5C, respectively recording the last cycle discharge capacity and dividing by the 1 st cycle discharge capacity to obtain cycle retention rate, wherein the test results respectively corresponding to the embodiments 1, 2 and 3 are shown in fig. 19, 20 and 21; the battery rate discharge performance is tested at the room temperature of 25 ℃, the battery rate discharge performance is respectively carried out at the charge and discharge rates of 0.2C/0.2C, 0.5C/0.2C, 1.0C/0.2C, 2.0C/0.2C and 3.0C/0.2C, the charge and discharge capacity retention rate is calculated, and the experimental results respectively corresponding to the embodiments 1, 2 and 3 are shown in figure 22, figure 23 and figure 24.
As can be seen from fig. 16, the ac impedance of the battery containing the polycrystalline anode material coated with nano-graphene according to the present invention is significantly reduced compared to the battery containing the polycrystalline anode material before coating; as can be seen from fig. 17, the ac impedance of the battery containing the polycrystalline anode material coated with the micron-sized graphene is reduced to a certain extent compared with that of the polycrystalline anode material battery before coating; as can be seen from fig. 18, the ac impedance of the battery containing the micro-nano-sized graphene-coated polycrystalline positive electrode material was significantly reduced as compared with the battery containing the polycrystalline positive electrode material before coating.
As can be seen from fig. 19 to 21, the battery of the graphene-coated polycrystalline positive electrode material provided by the present invention has a higher cycle capacity retention rate at 45 ℃ than the battery of the polycrystalline positive electrode material before coating; the preferable performance test chart of the embodiment shows that the nano-graphene-coated improvement effect is remarkable, but the micron improvement effect is remarkable, the capacity retention rate can reach more than 85% after 150 cycles at 45 ℃, and the nano-graphene-coated polycrystalline positive electrode material is remarkably improved.
As can be seen from fig. 22 to 24, the high-rate discharge capacity retention rate of the graphene-coated polycrystalline positive electrode material battery provided by the invention is higher than that of the polycrystalline positive electrode material battery before coating; in the preferable example performance test chart, it can be seen that the improvement effect of nano-graphene coating is very significant, the charge capacity retention rate of 1.0C/0.2C can reach more than 96%, the micron improvement effect is general, and the improvement effect of the micro-nano graphene coated polycrystalline positive electrode material is significant.

Claims (10)

1. A preparation method of a polycrystalline anode material modified in a tight coating mode is characterized by comprising the steps of mixing a graphene-coated polycrystalline anode material with a conductive agent and a binder, adding N-methyl pyrrolidone to adjust solid content, and coating the mixture on a current collector to obtain the graphene-coated polycrystalline anode material; the graphene-coated polycrystalline positive electrode material, the conductive agent and the binder are mixed according to the mass ratio of (90-99): (0.5-5): (0.5-5).
2. The method for preparing the close-clad modified polycrystalline cathode material according to claim 1, wherein the conductive agent is selected from one or more of carbon-based materials, metal-based materials and conductive polymers.
3. The method of claim 1, wherein the binder is selected from one or more of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, polyvinyl fluoride, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon.
4. The method for preparing a tightly-clad modified polycrystalline positive electrode material according to claim 1, wherein the current collector is an aluminum foil.
5. The method for preparing the close-coating modified polycrystalline cathode material according to claim 1, wherein a TEM image of the graphene-containing coated polycrystalline cathode material satisfies the attached drawings 1-3.
6. The method for preparing the tightly-coated modified polycrystalline positive electrode material according to any one of claims 1 to 5, wherein an SEM image of the graphene-containing coated polycrystalline positive electrode material satisfies the attached figures 4 to 6.
7. The method for preparing the polycrystalline cathode material modified in the close coating manner according to claim 6, wherein the coating thickness of graphene on the surface of the polycrystalline cathode material in the graphene-coated polycrystalline cathode material is less than 10 nm.
8. The method for preparing the close-coating modified polycrystalline positive electrode material according to claim 6, wherein graphene in the graphene-coated polycrystalline positive electrode material is closely attached to the surface of the positive electrode material, and the attachment gap is less than 3 nm; preferably, the fit clearance between graphene in the graphene-coated polycrystalline positive electrode material and the surface of the positive electrode material is almost 0 nm.
9. The method for preparing the close-coating modified polycrystalline cathode material according to claim 6, wherein the included angle between graphene in the graphene-coated polycrystalline cathode material and a tangent line of the graphene at a contact point of the cathode material is less than 5 °; preferably, the included angle between the graphene in the graphene-coated polycrystalline positive electrode material and the tangent line of the graphene at the contact point of the positive electrode material is almost 0 °.
10. The method according to claim 6, wherein the method comprises: mixing glue solution containing graphene with a positive active substance to obtain slurry, and drying the slurry to obtain a positive material; the positive active material exhibits a polycrystalline morphology comprising LiCoO2And/or LiNixCoyMnzO2And/or LiNixCoyAlzO2X + y + z is 1, x is more than or equal to 0.2 and less than or equal to 0.95, y is more than or equal to 0.05 and less than or equal to 0.4, and z is more than or equal to 0.05 and less than or equal to 0.5; the crystal structure is layered and belongs to the R-3m space group.
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